Transcript Stellar Winds and their Interaction with the Interstellar Medium

Stellar Winds and their Interaction with the
Interstellar Medium
Brian E. Wood (Naval Research Laboratory)
Jeffrey L. Linsky (JILA, University of Colorado)
OUTLINE
I. Astrospheric and Heliospheric
Evolution Associated with
Solar/Stellar Wind Evolution
A. Intro to Basic Heliospheric Structure
B. How Can We Detect Stellar Winds and/or
Astrospheres?
C. Inferring Wind Evolution from
Astrospheric Absorption
D. Planetary Implications for Wind Evolution
Neutrals interact
through simple charge
exchange processes
(e.g., Ho+H+ →H++Ho)
II. Astrospheric and Heliospheric
Evolution Associated with ISM
Variability (Linsky)
Neutral Diagnostics of the Outer Heliosphere
BISM
Heliopause
VISM
Termination
Shock
“Post-TS Neutralized
Pick-Up Ions”
Tail
Schwadron et al. 2011, ApJ, 731, 56
Neutral Diagnostics of the Outer Heliosphere
BISM
Heliopause
VISM
Termination
Shock
“The Ribbon,” presumably
where BISM n=0
“Post-TS Neutralized
Pick-Up Ions”
Tail
Schwadron et al. 2011, ApJ, 731, 56
Schwadron et al. 2011, ApJ, 731, 56
Neutral Diagnostics of the Outer Heliosphere
Linsky & Wood 1996, ApJ, 463, 254
 Cen
“Hydrogen Wall,” or
“Post-BS Neutralized ISM”
BISM
Heliopause
VISM
Termination
Shock
“The Ribbon,” presumably
where BISM n=0
“Post-TS Neutralized
Pick-Up Ions”
Tail
Schwadron et al. 2011, ApJ, 731, 56
Schwadron et al. 2011, ApJ, 731, 56
Neutral Diagnostics of the Outer Heliosphere
Linsky & Wood 1996, ApJ, 463, 254
 Cen
“Hydrogen Wall,” or
“Post-BS Neutralized ISM”
Wood et al. 2007, ApJ, 657, 609
1 Ori
“Post-TS Neutralized
Bulk Solar Wind”
BISM
Heliopause
VISM
Termination
Shock
“The Ribbon,” presumably
where BISM n=0
“Post-TS Neutralized
Pick-Up Ions”
Tail
Schwadron et al. 2011, ApJ, 731, 56
Schwadron et al. 2011, ApJ, 731, 56
Astrosphere Images
Young Star (LL Ori)
Red Supergiant (Betelgeuse)
Red Supergiant (Mira)
Massive Hot Star
Pulsar
But unfortunately we cannot detect the astrosphere of a Sun-like star like this!
HD151515 (O7 II)
Spectroscopic Diagnostics of
Stellar Winds
C IV
Mg II
Methods for Detecting and Studying the Solar Wind
Aurora
Comet tails
Direct spacecraft measurement
Coronal imaging
ACE (Advanced Composition Explorer)
Evolution of the Solar X-ray and EUV FLux
Ribas et al. 2005, ApJ, 622, 680
The Case for a Very Strong Wind for the Young Sun
1. The young Sun would have been much
more coronally active, with higher
coronal densities, so one would
intuitively expect a stronger wind.
2. Aside from the quiescent wind, the
stronger and more frequent flares of the
young Sun should by themselves lead to
a massive CME-dominated wind.
Example: Due to CMEs alone, Drake et
al. (2013) predict Ṁ=150 Ṁʘ for the 500
Myr old solar analog 1 UMa.
Conclusion: There is every reason to
believe the solar wind must have been
much stronger in the past.
Drake et al. 2013, ApJ, 764, 170
The Case for a Relatively Weak Wind for the Young Sun
Solar activity varies significantly over the course
of its activity cycle, but:
1. Voyager has observed little variation from
the canonical solar mass loss rate of
Ṁʘ=2×10-14 Mʘ/yr.
2. There is no strong correlation between solar
X-ray flux and mass loss rate.
Conclusion: Perhaps the solar wind is
relatively constant over time.
Cohen 2011, MNRAS, 417, 2592
astrospheric
absorption
heliospheric
absorption
Models of the  Cen Astrosphere
Ṁ=0.2 Ṁ⊙
Ṁ=0.5 Ṁ⊙
Ṁ=1.0 Ṁ⊙
Ṁ=2.0 Ṁ⊙
Astrospheric Absorption Predictions for  Cen
Wood et al. 2001, ApJ, 547, L49
Wood et al. 2002, ApJ, 574, 412
Astrospheric Models
The ε Eri astrosphere is comparable in
size to the full moon in the night sky!
The New 1 UMa Measurement
• 1 UMa and 3 other young Sun analogs observed
by HST in 2012.
• Only 1 UMa provided an astrospheric detection.
• 1 UMa (G1.5 V) is a 500 Myr solar analog.
• The absorption suggests a mass loss rate of only
0.5 Ṁʘ (Wood et al. 2014, ApJ, 781, L33).
List of Astrospheric Measurements
Mass Loss/X-ray Relation
Red: Solar-like GK main sequence stars
Green: M dwarfs
ṀFX1.340.18
Wood et al. 2014, ApJ, 781, L33
Is Magnetic Topology Inhibiting the
Winds of Young, Active Stars?
Rice & Strassmeier 2001, A&A, 377, 264
Wind Evolution for a Sun-like Star
Ṁt-2.330.55
Evolution of the Martian Atmosphere
Mars 4 Gyr ago
Mars Today
What Role do Magnetospheres Play in
Atmospheric Evolution?
Earth is protected by a
“magnetosphere,” but
Mars is not!
Lundin 2001, Science, 291, 1909
Stellar Wind Erosion of a “Hot Jupiter”
This is just an artist’s conception
of a stellar wind eroding a
planetary atmosphere, but Ly
absorption from such an eroding
atmosphere may have actually
been detected for the transiting
exoplanet HD 209458b (VidalMadjar et al. 2003, Nature, 422,
143; Linsky et al. 2010, ApJ, 717,
1291).
The Faint Young Sun Problem (FYSP)
(first defined by Sagan & Mullen 1972, Science, 177, 52)
Bahcall et al. 2001, ApJ, 555, 990
Could the FYSP be Resolved by a More Massive Young Sun?
Sackmann & Boothroyd
2003, ApJ, 583, 1084
Mass Lost due to Solar Wind Inferred from
Astrospheric Measurements
Could a Stronger Wind for the Young Sun Explain the
FYSP Via Cosmic Ray Cooling?
Shaviv 2003, JGR, 108, 1437
SUMMARY
• Currently the only way to study the astrospheres and winds of solar-like
stars is through astrospheric Lyα absorption observed by HST.
• Analysis of the astrospheric absorption suggests that for solar-like GK
dwarfs, mass loss and activity are correlated such that ṀFX1.340.18.
• However, this relation does not extend to high activity levels (FX>106 ergs
cm-2 s-1), possibly indicating a fundamental change in magnetic structure
for more active stars.
• The mass-loss/activity relation described above suggests that mass loss
decreases with time as Ṁt-2.330.55. However, the apparent high activity
cutoff means that this mass loss evolution law doesn’t extend to times
earlier than t~0.7 Gyr.
• Despite the higher mass loss rates predicted for the young Sun by our
mass loss evolution law, the total mass lost by the Sun in its lifetime is still
insignificant, so this stronger young wind can’t directly solve the Faint
Young Sun problem, though there is speculation that it could indirectly via
cosmic ray attenuation.
• The existence of generally stronger winds at younger stellar ages makes it
more likely that solar/stellar wind erosion plays an important role in the
evolution of planetary atmospheres.